Modern integrated circuits are fabricated using a wide variety of processes, many of which are performed under high vacuum conditions. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
Conventionally, high vacuum system components, such as electron beam columns and associated components, are fabricated from stainless steel, which has both relatively good mechanical performance and relatively good vacuum performance, and which is easy to machine. However, stainless steel has a relatively poor field shielding performance, and is prone to being magnetized. In order to resolve these relatively poor field shielding issues, two approaches are typically applied.
First, the component is made with iron and nickel-iron alloys. However, due to the high out gassing rate of such materials and the difficulty in making a knife-edge vacuum seal from such materials, achieving an ultra high vacuum level is very challenging if not impossible. Second, one or more Mu-metal sheet layers are used to provide field shielding for a stainless steel component. However, the resulting shielding efficiency is very limited because the sheet Mu-metal material cannot be made very thick. Also, mechanical vibration can be extremely destructive to such layered structures.
Titanium is often used to fabricate non-magnetic components that need to provide good field shielding, such as those that are disposed close to an electron beam path, and more especially for those parts immersed in the magnetic field. However, titanium is hard to machine and difficult to weld to other commonly used materials, like stainless steel and nickel-iron alloys. Thus, titanium parts are typically fabricated separately and then mechanically fastened into the high vacuum system, such as an electron beam column. This tends to create problems with proper alignment of the various components.
Another issue with the materials that are currently used in high vacuum systems is the amount of particulates that are generated by moving surfaces in non-magnetic but electrically conductive high vacuum applications. Moving components in such applications are typically highly polished and coated with low friction ceramics, such as titanium-nitride and hard chromium-diamond binary. In some applications, doped polytetrafluoroethylene is applied to sliding surfaces. Ceramic balls, such as silicon-carbide, silicon-nitride, sapphire, and aluminum-nitride have also been used.
Unfortunately, such materials tend to experience a relatively high rate of wear, and tend to shed a relatively large amount of particles into the high vacuum system. Such worn surfaces also cause relatively high levels of uncontrolled stiction, meaning that the desired smooth-sliding motion becomes susceptible to a “stick then slip” behavior that adversely affects the accuracy and precision of the sliding mechanisms. Further, the loose, non-conducting particles that are shed can become charged in certain applications, causing contamination and electrical problems.
What is needed, therefore, is a system that overcomes problems such as those described above, at least in part.